U.S. Pat. No. 4,388,668 describes a capacitive pressure sensor comprising:
a substrate made of ceramic material, PA1 a diaphragm made of ceramic material, PA1 leads PA1 a substrate made of ceramic material, PA1 a first and second diaphragm made of ceramic material, PA1 a hole connecting the two cavities and leading through the substrate and outwards, PA1 a substrate made of ceramic material, PA1 a diaphragm made of ceramic material, PA1 leads PA1 a substrate made of ceramic material, PA1 a first and a second diaphragm made of ceramic material, PA1 leads, PA1 a hole connecting the two cavities, leading at least through the substrate and outwards,
on the one surface of which PA2 which is permanently joined and pressure-sealed to the substrate by means of an original glass frit acting as a spacer holding the diaphragm and the substrate at a defined distance from each other to form a cavity, and PA2 which on the surface facing the substrate is provided with a second metallic electrode; and PA2 which extend inwards to the electrodes in the region of the spacer. PA2 whose surfaces facing away each other--the first and second surfaces--support PA2 which are permanently joined and pressure-sealed to the first and second surfaces of the substrate, respectively, by means of an original glass frit acting as a spacer holding the diaphragms and the substrate at defined distances from each other to form a first and second cavity, respectively, and PA2 which on each cavity side are provided with a second and a fourth metallic electrode, respectively; and PA2 the two cavities and the hole being filled with oil. PA2 on one surface of which PA2 which is permanently joined and pressure-sealed to the substrate by means of the original glass frit acting as a spacer holding the diaphragm and the substrate at a defined distance from each other to form a cavity, and PA2 which on the cavity side is provided with a second metallic electrode; and PA2 which extend inwards and/or through the diaphragm to the electrodes in the region of the spacer. PA2 whose surfaces facing away each other--the first and second surfaces--support PA2 which are permanently joined and pressure-sealed to the first and second surfaces of the substrate, respectively, by means of the original glass frit acting as a spacer holding the diaphragms and the substrate at defined distances from each other to form a first and a second cavity, respectively, and PA2 which on each cavity side are provided with a second and a fourth metallic electrode, respectively; PA2 which extend inwards and/or through the first and the second diaphragm, respectively, or through both diaphragms to the respective electrodes; and PA2 the two cavities and the hole being filled with oil.
a first metallic electrode is disposed in direct contact with the substrate; PA3 a first metallic electrode and a third metallic electrode, respectively, each being in direct contact with the substrate; PA3 a first metallic electrode is disposed and PA3 a glass layer formed from an original glass frit is disposed at least on the first metallic electrode; PA3 a first metallic electrode and a third metallic electrode, respectively, PA3 a first glass layer formed from an original glass frit at least on the first metallic electrode, PA3 a second glass layer formed from the original glass frit at least on the third metallic electrode;
Further, U.S. Pat. No. 4,531,415 describes a capacitive differential pressure sensor, comprising:
With the two types of pressure sensors mentioned, the prevention of short-circuits between the electrodes facing each other is important. Such short-circuits may be caused by material particles coming between the electrodes during manufacture and not being discovered there, or during operation by pressures which are higher than the pressure admissible for a concrete type of pressure sensor and which thus lead to contact between the electrodes, or through parts of the electrodes detaching themselves from the diaphragm and/or substrate and contacting each other again.
According to U.S. Pat. No. 4,531,415 already mentioned, an attempt was made to solve the short-circuit problem by fixing to the substrate some parts of insulating material protruding from the electrodes as projections, so that in case of an inadmissible high pressure the electrodes of the diaphragm can be intercepted by the projections and thus cannot touch the electrodes of the substrate.